This is a proposal to complete retesting of lung function in two of four demographically matched cohorts and to complete analysis of results in all four cohorts. The 15,164 cohort members live in four areas of Los Angeles which have been historically and concurrently exposed to 1) moderate levels of photochemical oxidants, 2) high levels of secondary pollutants including photochemical oxidants, 3) SO2/particulates, and 4) minimal levels of pollutants. Pollutant levels are continuously measured by monitoring stations of the Southern California Air Quality Management District located within or adjacent to the study areas. Lung function tests administered at the mobile laboratory include spirometry, single breath nitrogen washout curve and plethysmography. Tests are readministered to a 4% sample at the UCLA Pulmonary Function Laboratory to determine reliability and identify fixed errors which may arise at the mobile laboratory. Baseline testing in all four areas and retesting in two areas will have been completed by 1980. Results of baseline testing were worse in the three areas exposed to pollutants. The two cohorts still to be retested were those with the poorest lung function results at baseline and which have been exposed to pollutant mixes distinctly different from the first two areas retested. The major objectives are to determine 1) if long-term exposure to photochemical oxidants and other pollutants is associated with the initiation and/or promotion of respiratory impairment and/or chronic respiratory disease, 2) which of the lung function tests administered (questionnaire, spirometry-air and He/O2, single breath nitrogen washout curve and body plethysmography) are specific and/or sensitive early indicators of impaired lung function and which are most suitable for use in field surveys.